1. Field of the Invention
The present invention relates to subsurface well apparatus and more particularly to the remote operation of subterranean well tools.
2. Summary of the Prior Art
Subsurface well tools have been operated in the past by a wide variety of mechanisms. Manipulation of the tubing string, such as push and/or pull, tubular rotation, and the like, is one of the more common methods employed, but can be difficult to accurately accomplish in deep or deviated wells. Other actuation means include use of hydraulic/hydrostatic members, pneumatic elements, as well as radio and other surface and subsurface-initiated electronic components.
Typical of subterranean well tools actuated by such procedures include bridge plugs, packers, perforating guns, tubing hangers, safety and other valves, test trees, and the like, all of which are contemplated for use with the present invention. Such tools require actuation procedures, such as setting at correct depth in the well and at a particular time during the completion operation, unsetting in response to a given well condition or event, re-setting, opening, closing or throttling flow paths, perforating casing, and the like.
In the normal operation of a well wherein the production tubing or work string is installed or being installed, and the tools are to be activated by hydraulic means incorporating fluid and pressure within the production or work string, it is very common to provide one or more ports in the wall of the production tubing or work string, or a component in direct fluid communication therewith, to provide actuating fluid from the bore of the production tubing to well tools to initiate the desired operation, such as the setting of a packer. It has been found that such openings provided in the wall of the production tubing or work string are highly undesirable because such openings must be effectively sealed against any leakage of any fluids subsequently carried through the tubing, such as the produced well fluids. Seals that are employed in and between operating components of well tools, such as pistons and housings therefor, are subject to deterioration, hence leakage, because of the high temperature, high pressure environment in which such seals are required to operate regardless of whether such seals are elastomeric, metallic, or any other commonly used structures. This is particularly true of the seals employed on actuating pistons for packers, safety valves or similar downhole tools wherein an actuating fluid is applied to one side of the piston and the other side of the piston is exposed to well fluids, atmospheric pressure, or the like. Deterioration of the seals on such actuating member expose such components to undesirable leakage of either actuating fluid or production or other fluids, depending on the relative pressures, around the piston, or other actuating component, thus initially creating a microannulus therethrough. Such micro-annulus leak path could be serious enough to subject the well to a blow out.
The utilization of a downhole energy source which can be transformed into kinetic energy by the provision of a triggering signal to operate a well tool is disclosed in U.S. Pat. No. 3,233,674. In the illustrated device thereof, the downhole source of energy is an explosive charge which is discharged and the resulting gas is applied to a piston which functions to set a hanger in a well casing. The triggering signals for energizing the downhole circuitry for effecting the discharge of the explosive charge is produced by a pair of sonic frequency generators which are located at the surface and which are transmitted downhole through well fluids or a tubing string, or can be packaged with a suitable power supply container that is lowered into the well on wireline or cable.
One problem with apparatus constructed in accordance with U.S. Pat. No. 3,233,674, is that the acoustical signals employed for effecting the triggering of the downhole source of energy must be coded in order to prevent inadvertent operation of the device by the static normally encountered in the transmission of acoustic signals either through the well fluids or through the body of a tubular conduit. The employment of coded alternating signals necessarily complicates the electronic pickup circuitry which must be designed so as to distinguish between static signals and the proper coded signal.
U.S. Pat. No. 4,896,722 discloses another approach to energization of a downhole source of energy. In the apparatus illustrated in this patent, the hydrostatic pressure of well fluids in the well annulus acts on a floating piston to provide the source of downhole energy. Such energy is employed to effect the opening and closing of a test valve which is normally utilized in the lower end of a string of drill stem testing tools. The hydrostatically pressurized oil acts on one side of a piston which is opposed on its opposite side by air at atmospheric or other low pressure. The piston is prevented from movement by a spring until a predetermined hydrostatic annulus pressure is obtained. A pair of solenoid controlled valves controls the hydrostatic pressure acting on the floating piston. The two solenoid control valves are in turn controlled by a microprocessor which operates in response to a pressure transducer which is exposed to annulus pressure and provides an electrical signal output indicative thereof. Again, however, the signals applied to the pressure transducer are in the nature of a series of low level pressure pulses, each having a specified duration. Such pulses are applied at the well surface to the fluids standing in the well annulus. Thus, the detection circuitry which picks up the signals is complicated because it has to be designed to respond to only a specific series of low level pressure pulses.
The prior art has not provided an actuating system for a downhole well tool which does not require ports in the production tubing or work string or component in fluid communication therewith, and which may be reliably controlled from the surface through the utilization of control forces through the wall of the production tubing or work string to produce an activating signal for actuating the downhole well tool by a downhole energy source and to block fluid communication between an actuating fluid body and a second fluid source within said well across dynamic seals between actuating members of the well tool.